我们可以利用psql命令来查询sql语法。

切换到Postgresql用户下，

<span style="font-size:18px;">[doctor@localhost ~]$ su - postgres 
密码：
su: 鉴定故障
[doctor@localhost ~]$ su - postgres 
密码：
-bash-4.3$ bash
bash-4.3$ psql 
psql (9.4.2)
输入 "help" 来获取帮助信息.

postgres=# 

postgres=# help
您正在使用psql,这是一种用于访问Postgresql的命令行界面
键入： \copyright 显示发行条款
 \h 显示 sql 命令的说明
 \? 显示 pgsql 命令的说明
 \g 或者以分号(;)结尾以执行查询
 \q 退出
postgres=# 



</span>

<span style="font-size:18px;">postgres=# \h
可用的说明：
  ABORT                            DEALLOCATE
  ALTER AGGREGATE                  DECLARE
  ALTER COLLATION                  DELETE
  ALTER CONVERSION                 DISCARD
  ALTER DATABASE                   DO
  ALTER DEFAULT PRIVILEGES         DROP AGGREGATE
  ALTER DOMAIN                     DROP CAST
  ALTER EVENT TRIGGER              DROP COLLATION
  ALTER EXTENSION                  DROP CONVERSION
  ALTER FOREIGN DATA WRAPPER       DROP DATABASE
  ALTER FOREIGN TABLE              DROP DOMAIN
  ALTER FUNCTION                   DROP EVENT TRIGGER
  ALTER GROUP                      DROP EXTENSION
  ALTER INDEX                      DROP FOREIGN DATA WRAPPER
  ALTER LANGUAGE                   DROP FOREIGN TABLE
  ALTER LARGE OBJECT               DROP FUNCTION
  ALTER MATERIALIZED VIEW          DROP GROUP
  ALTER OPERATOR                   DROP INDEX
  ALTER OPERATOR CLASS             DROP LANGUAGE
  ALTER OPERATOR FAMILY            DROP MATERIALIZED VIEW
  ALTER ROLE                       DROP OPERATOR
  ALTER RULE                       DROP OPERATOR CLASS

postgres=# \h select
命令：       SELECT
描述：       从资料表或视观表读取资料
语法：
[ WITH [ RECURSIVE ] with查询语句(with_query) [,...] ]
SELECT [ ALL | DISTINCT [ ON ( 表达式 [,...] ) ] ]
    [ * | 表达式 [ [ AS ] 输出名称 ] [,...] ]
    [ FROM from列表中项 [,...] ]
    [ WHERE 条件 ]
    [ GROUP BY 表达式 [,...] ]
    [ HAVING 条件 [,...] ]
    [ WINDOW 窗口名称 AS ( 窗口定义 ) [,...] ]
    [ { UNION | INTERSECT | EXCEPT } [ ALL | DISTINCT ] 查询 ]
    [ ORDER BY 表达式 [ ASC | DESC | USING 运算子 ] [ NULLS { FIRST | LAST } ] [,...] ]
    [ LIMIT { 查询所用返回记录的最大数量 | ALL } ]
    [ OFFSET 起始值 [ ROW | ROWS ] ]
    [ FETCH { FIRST | NEXT } [ 查询所用返回记录的最大数量 ] { ROW | ROWS } ONLY 
]
    [ FOR { UPDATE | NO KEY UPDATE | SHARE | KEY SHARE } [ OF 表名 [,...] ] [ N
OWAIT ] [...] ]

from 列表中的项可以是下列内容之一

    [ ONLY ] 表名 [ * ] [ [ AS ] 化名 [ ( 列的化名 [,...] ) ] ]
    [ LATERAL ] ( 查询 ) [ AS ] 化名 [ ( 列的化名 [,...] ) ]
    WITH查询语句名称(with_query_name) [ [ AS ] 化名 [ ( 列的化名 [,...] ) ] ]
    [ LATERAL ] 函数名称 ( [ 参数 [,...] ] )
                [ WITH ORDINALITY ] [ [ AS ] 化名 [ ( 列的化名 [,...] ] ) [ AS ] 化名 ( 列定义 [,...] )
    [ LATERAL ] 函数名称 ( [ 参数 [,...] ] ) AS ( 列定义 [,...] )
    [ LATERAL ] ROWS FROM( 函数名称 ( [ 参数 [,...] ] ) [ AS ( 列定义 [,...] )
 ] [,...] )
                [ WITH ORDINALITY ] [ [ AS ] 化名 [ ( 列的化名 [,...] ) ] ]
    from列表中项 [ NATURAL ] 连接操作的类型 from列表中项 [ ON 用连接操作的条件 |
 USING ( 用于连接操作的列 [,...] ) ]

with查询语句是：

    WITH查询语句名称(with_query_name) [ ( 列名称 [,...] ) ] AS ( 查询 | 值 | in
sert | update | delete )

TABLE [ ONLY ] 表名 [ * ]

postgres=#  </span>